The supply of nitrogen for brown bean production is limited to 30 kg/ha if
the grower wishes to be eligible to receive subsidy from the EC. This limit
is not based on the nitrogen requirement of the bean crop and is so low th
at the application in many cases may be unnecessary. The current experiment
was designed to test the hypothesis that reduced nitrogen fertilisation in
the spring will not reduce the yield if beans have been grown on the field
previously and consequently the bacteria necessary for the nitrogen fixing
are available.
Three cultivars of dried brown beans were grown in the 1997 season. The soi
l analysis in the spring showed a content of 10 kg N ha(-1) previously mine
ralized nitrogen. In a low fertilised treatment 5 kg N/ha was added and in
a normal fertilised treatment 30 kg N/ha. No differences were found between
the treatments for any of the cultivars with respect to yield, number of n
itrogen-fixing nodules, or plant of dry matter and nitrogen contents. All e
xperimental plots contained about 9 kg N ha(-1) in the autumn.
This experiment indicates that an N-min content of 15 kg N ha(-1) might be
enough in the spring. If this figure can be confirmed in future experiments
it should be possible to omit nitrogen fertilisation on some fields, or du
ring years with abundant early nitrogen mineralization, without risking a r
educed yield.